There’s no shortage of sporting competitions and activities that require some acclimatisation to hot weather. At one extreme is the Marathon de Sables in the Sahara Desert, a gruelling multi-stage race totalling some 251km (156 miles), across inhospitable terrain, in a hot desert climate. It requires those taking part to prepare effectively to cope safely and perform in such hot conditions.

Training in hot weather isn’t without risk and sometimes it can be an occupational hazard – this was clearly demonstrated with the deaths of two soldiers on an SAS selection weekend in the Welsh Brecon Beacons when temperatures in July 2013 rose well above 30°C. But it is well established that repetition of heat stress exposure can aid adaptations to the heat. For example it can produce a lower body temperature, reduced heart rate, increased sweat rate for cooling, resulting in an increase in human performance.

The most effective way to prepare for performance in the heat is to actually travel to the hot country where the event is taking place and ideally allow 14-days exposure before competing, to allow the human body to fully adapt. However, many people preparing for performance or relocation to hot climates often have time and financial restrictions placed upon them. Therefore, the question that arises is, what can we do to prepare effectively before embarkation to hot climates in our own country, if it has only temperate weather conditions that we experience in the UK?

Using an environmental chamber

Many elite performers and the military occupations may benefit from the use an environmental chamber to acclimatise “artificially” to the heat, before travelling to the hot country. However, many training methods in such facilities tend to use a fixed work intensity, incorporate continuous exercise, are long-term in duration (more than seven days) and use hydration. However, a great deal of occupational work, including that of the military, tends to involve intermittent activity and have limited time available in the preparation for hot conditions. For example, members of the military often have to relocate to hot climates at short notice and they would be expected to carry out their daily activities at the same intensity of cooler conditions back at home in the UK.

Our research using a state-of-art environmental chamber in the Department of Sport, Health and Exercise Science, at the University of Hull has recently investigated the effectiveness of short-term (five-day) heat acclimation on intermittent exercise in hot and cool environments.

We used ten, male, trained participants who underwent 90 minutes heat exposure, with no fluid intake, for five consecutive days at 39.5 degrees centigrade (60% humidity). During each acclimatisation session there was approximately 30 minutes cycling exercise, controlled by maintaining body-core temperature at 38.5 degrees centigrade and measured using a rectal probe. Before and after the five-day heat acclimatisation, we carried out an exercise test on participants that consisted of 45-minute, intermittent exercise in hot (31 degrees centigrade) and cool (11 degrees centigrade) conditions. This exercise test was adapted from exercise intensities experienced by professional football players and involved repeated maximal sprinting. This was then followed by a running, incremental test to exhaustion as a measure of endurance performance.

Sprint exercise pedal rotation. Dr Andrew Garrett

We found using this short-term heat acclimation method for five days, it was effective for physiological adaptation in a hot environment. Lower body-core temperature, reduced heart rate response and perception of exercise intensity was observed. Therefore, our work suggests that by restricting fluid intake during heat acclimation, in a controlled manner, we have enhanced the adaptation of the fluid-regulatory system which acts to maintain hydration status in the human body. This may have been a key factor in the increase in intermittent sprint and endurance exercise performance observed in both the hot and cool conditions.

Our work shows that short-term heat acclimatisation of five days is effective for sprint and endurance exercise in the heat and it may be a beneficial training method for the preparation of performance in the cool temperate conditions that we experience in the UK.

This information may not only be of use for elite sports people in the preparation for sports performance in different climates but maybe of use for occupational activities – such as the preparation for military excursions into hot countries. This could have training implications for the potential benefits of warm weather training camps.